With development of a wireless mobile communication technology, electronic products are embedded with a wireless mobile communication system and a wireless sensor system. An antenna is a chief communication component for determining capability of the wireless communication products. Meanwhile, an IEEE 802.15.4/4a wireless communication system has found a growing application in detection and control systems such as home automations and office automatic sensors. For now, the IEEE 802.15.4 wireless communication system has been commercialized at a bandwidth of 2400 MHz. However, the IEEE 802.15.4 system for 2400 MHz bandwidth may experience interference with the existing wireless LAN frequency. Therefore, the IEEE 802.15.4 system for 900 MHz bandwidth is being developed at home. This crucially necessitates a dual band antenna for covering both bandwidths of 900/2400 MHz for the IEEE 802.15.4 system and the IEEE 802.15.4a system which is to be standardized later.
Conventionally, the IEEE 802.15.4 wireless communication system mainly employs a monopol or helical antenna, and a ceramic chip antenna in the applications thereof to reduce size. However, the external antenna is easily altered in its characteristics by external environment, while the internal ceramic chip antenna degrades capability of the wireless communication system due to decline in gain thereof. Moreover, a separate antenna is required for each of the IEEE 802.15.4/4a wireless communication modules, thereby creating additional costs.